This invention relates to fuel dispensing nozzles of the type used to dispense gasoline into automobiles and the like, and more particularly to an improvement in the shut-off apparatus that prevents nozzle failure when the nozzle is quickly activated and prevents premature shut off due to slight changes in the pressure differential that activates the nozzle shut-off mechanism.
As is well known, gasoline dispensing nozzles of the type found at most service stations include a spout which is inserted into the inlet of the filler pipe of an automobile's fuel tank. Generally the nozzle has a fluid flow path to allow fuel to flow through the nozzle and out through the spout. Recently, in response to environmental concerns, conventional nozzles are designed with a vapor flow path to capture fuel vapors and return them to the fuel dispensing system to avoid release of the vapors into ambient air. Conventional nozzles incorporate a popper valve apparatus in the fluid flow path to control the main flow of fuel through the nozzle. This valve apparatus is activated to open when the customer lifts the handle or lever to begin dispensing fuel. The lever abuts a poppet stem and pushes the poppet valve off its seat thereby opening the fuel flow pathway.
Generally, conventional nozzles have an automatic shut off assembly within the nozzle to close the poppet valve in response to a change in pressure, for example, when excessive pressure is encountered, or when the fuel level in the vehicle gas tank reaches a full condition. A conventional automatic shut off assembly contains a plunger that is retained in an up, or nozzle opened position within the nozzle, when the lever is activated to open the poppet valve to permit fluid fuel flow through the nozzle. However, when the plunger drops to a down nozzle closing position, it functions as as an alternate pivot point, relieving lever pressure on the poppet valve, thus allowing the valve to close and immediately shut off the flow of fuel through the fuel flow pathway.
The plunger is moved to the up or nozzle opening position by a spring means, and connects at its bottom end to the front of the lever that urges when activated the poppet valve to open. The plunger has a plurality of retainer balls seated in clearance slots at an upper end that are outwardly biased by an enlargement on a latch pin which seats within the upper end of the plunger. The outwardly biased retainer balls engage a latch ring and thus hold the plunger in the up position. The latch pin is connected to and moves with a superposed diaphragm housed in a vacuum forming chamber above the plunger. The vacuum chamber is in pressure communication with a venturi located in the spout. A change of pressure at the venturi creates a low pressure or vacuum in the chamber thus drawing the diaphragm upward, when the vented end of the spout is blocked due to dispensing fuel reaching a full capacity in the tank. The attached latch pin lifts from the plunger upwardly allowing the retaining balls to recede into their seats within the plunger. The plunger then slips below the latch ring and drops into its secondary or lever dropping position thus pushing the lever away from a poppet valve stem and allowing the poppet valve to close, immediately shutting off fluid flow.
The conventional automatic shut-off assemblies have several drawbacks. Due to tolerances in the various parts of the diaphragm assembly, the associated latch pin and its plunger, and also due to the positioning of the latch ring, there is some travel by the plunger before the retaining balls engage the latch ring. This movement or travel is referred to as "loss motion". Moreover, the diaphragm, with the conventional latch pin attached thereto, must move downward upon activation of the lever so that the latch pin seats within the plunger to effectively bias the retaining balls to engage the latch ring and hold the plunger in the lifted and nozzle opening position. The vacuum chamber above the diaphragm generally has two small ports to vent through. In order for the diaphragm, and the associated latch pin, to move downward, air has to enter the chamber through the small port at the tip of the nozzle spout to equalize the pressure and allow the diaphragm to also equalize. When a customer quickly activates the nozzle lever, the plunger is jarred and the latch mechanism retaining balls are held above the level of the latch ring and then descends slightly to the point where the retaining balls can engage the latch ring. This slight downward movement is the "loss motion". The plunger, however, moves downward toward the latch ring faster than the diaphragm can move, due to the slow displacement of air in the vacuum chamber, and the latch pin, connected to the diaphragm, does not always engage the plunger to bias the retaining balls outward. Therefore, sometimes the plunger slips below the latch ring to its closed position thereby preventing the poppet valve from opening. This can be frustrating to the customer who must actuate the lever several times and eventually actuate the lever more slowly so that the diaphragm, and the associated latch pin, has sufficient time to set up and slightly shift downward and engage the plunger to hold the plunger in the up or nozzle opening position.
Furthermore, since the latch pin moves directly with the diaphragm, any change in pressure in the vacuum chamber above the diaphragm will cause the diaphragm to rise, drawing the latch pin away from the retainer balls. The balls recede into their seats in the plunger and the plunger falls below the latch ring, shutting off fluid flow. Although this is the functional objective of the automatic shut-off assembly when the tank is full, it can be frustrating if the shut-off occurs prematurely. For example, if fluid splashes up from the tank onto the vent ports located on the spout, a slight pressure differential can be created in the associated vacuum chamber and the diaphragm prematurely moves slightly upward. The associated latch pin will also be pulled up and the plunger will drop, undesirably shutting off fluid flow.
It would be advantageous, therefore, to have a latch pin operatively associated with the diaphragm that will not immediately move up with the diaphragm as the diaphragm moves upward in response to slight variations in the vacuum pressure, and provide some degree of play in the operations of these components, thereby creating a slight lag between the movement of the diaphragm and the movement of the latch pin. Very slight changes in pressure in the chamber above the diaphragm in response to splashing, for example, would not result in premature shut-off of fluid flow. However, normal vacuum changes due to a full gas tank will cause the diaphragm to effectively pull the latch pin out of its seat thereby causing the plunger to drop and thereby properly shut off fluid flow. Furthermore, it would be advantageous to have a latch pin operatively associated with the diaphragm that can move to some degree downwardly faster than the associated diaphragm so that the latch pin can move down with the plunger's loss motion and seat in the plunger as the balls effectively engage the latch ring to properly hold the plunger in the up position even though the diaphragm lags behind in its downward movement.